In recent years, the demand for semiconductor lasers has been increasing in the field of optical communication, laser printers, optical disks, and the like, and research and development therefor have been actively conducted mainly for those of the GaAs type and the InP type. In particular, in the field of optical information processing, a system for recording/reproducing information using particularly AlGaAs type semiconductor laser light having a wavelength of about 780 nm has been put to practical use, and has been widely used in a compact disk, and the like. Recently, however, a further increase in a storage capacity has been more in demand for these optical disk devices, and the need for implementation of a laser having a short wavelength has been increasing correspondingly.
In this respect, an AlGaInP type semiconductor laser can oscillate in a red range between about 620 nm and about 690 nm, producing light having the shortest wavelength among the semiconductor lasers which are at the current level of practical use, Accordingly, the AlGaInP type semiconductor laser is promising as a next-generation light source for large capacity optical information recording in place of the conventional AlGaAs type semiconductor laser.
A conventional semiconductor laser is disclosed by D. P. Bour et al. in the Journal of Quantum Electronics, vol. 30, No. 2, pp. 593-606 (February 1994). The semiconductor laser disclosed in this article includes an active layer having a multiple quantum well structure formed on a substrate, achieving an output of 5 mW at an oscillation wavelength of 680 nm.
However, as the oscillation wavelength is shortened, a bandgap in the active layer is increased, and an offset .DELTA.Eg of a bandgap between the active layer and a cladding layer is reduced correspondingly. Therefore, a carrier overflow due to current injection occurs, resulting in an increased threshold current and thus an increased operating current. Such a phenomenon is not preferable for implementing a higher output of the semiconductor laser.